Russ' Do It Yourself Home Workshop

Finding Fixes to Just About Anything and Everything

Archive for September, 2011

Replacing the Inverter Assembly on a 2002 1st Gen Prius

Posted by Russell Wright on September 18, 2011

As my wife and I were driving to Lowe’s the other day in my 2002 Prius, it suddenly started to shudder and run very rough.  We weren’t but about a mile or two from home, so we immediately turned around and limped home.  After we made it home, the car wouldn’t even start…it would simply shudder when starting was attempted. 

I went to the local Auto Zone and “borrowed” one of their code readers and found P3125 – Bad Inverter.  A quick search on the internet and I found the price for a dealer replacement was about $4500.  Ouch!

After further reading I also found that it may not be as simple as replacing the inverter, as P3125 can also mean other things.  So I decided I’d take it up to the Toyota dealer and let them diagnose the problem to see if our diagnoses agreed.  I got my brother-in-law to hook me up behind his Toyota Tundra with my tow strap and haul me the 8 miles to the dealership in Richardson.  $54 later, the dealership confirmed my diagnoses and quoted me about $4400 to replace it.  I asked if they would consider using my salvage part I purchased for $350 and they said, “No, too much liability.”  OK, I thought, I guess I’m on my own…

So we hauled it back and I finally got a round-tuit yesterday.  Since I couldn’t find a good procedure that anyone had documented online, I decided I’d document it and take a few pics along the way.  Here’s my result.

Disclaimer:  I R an electrical engineer, so I am comfortable working around electricity.  If you aren’t, perhaps you should befriend someone who is.  Engineers need friends, too!  Also, anywhere there were big orange HV cables I always checked the voltage between all connections with my meter before touching anything with a wrench.

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Before you start working on this car where you’ll be dealing with the high voltage (HV), you need to disable all the power and let it sit a few minutes to insure all the HV capacitors have had time to bleed down.  I’ve heard many time tables on this, such as “let it sit an hour,” but the Toyota dismantling manual states five minutes, so I figured by the time I got to working on that part plenty of time would have passed. 

First, disconnect the 12v “auxiliary” battery (located in the trunk) and pull the safety plug on the high voltage.  I disconnected the ground (-) battery cable.  Here are a few pics in the trunk showing the location of each.

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Pull the lever down to unlock the safety plug.

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Me pulling out the HV safety plug.  Hmmm, perhaps I should’ve worn insulating gloves (and a bunny suit).

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Now drain the inverter coolant.  It’s kinda’ scary because you might think you are going to drain the transmission fluid.  Oh, wait!  You will if you remove the wrong plug!  Don’t do that!  There are others that have much better photos of this.  Check out YouTube.

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Now you can remove the hoses to the inverter cooling system.

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As I started this process, I did things in the wrong order (of course) and found there were a couple of bolts I couldn’t get to.  I sent a text to the nice folks at Luscious Garage asking how I get to the bolts and they texted back (amazingly!) to remove the windshield wiper cowl.  Duh!  Should’ve done that at the very beginning.  My loss is your gain!

Remove the seal.

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The windshield wipers are held on with nuts that should be pretty easy to remove.  After the nuts are off, remove tension on the windshield wipers by pulling them away from the glass and see if you can’t easily remove them from the shafts. 

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The cover is essentially held on with two phillips screws (one on either side) and the fasteners that snap in the rubber seal.

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You do have to remove both sides of the cowl cover. 

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Once you get all this windshield wiper stuff out of the way, you can remove the cowl pan it sits in.  I didn’t get a picture of this for some unknown reason, but it’s pretty easy.  It just takes 5 or 6 bolts and you lift it out.  Be careful not to cut yourself (I did) on the sharp edges.

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Once you get the connectors out of the way you can get to the two gray connectors on the back and have easier access to the HV cable connectors (which can be somewhat difficult to wiggle loose, but be patient).

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